An ultrasonic transducer is used in, for example, a diagnostic apparatus of tumors in the human body. Conventionally, an ultrasonic transducer using the vibration of a piezoelectric body has been mainly used. However, with the recent advancement of MEMS (Micro Electro Mechanical System) techniques, a capacitance detecting ultrasonic transducer (Capacitive Micromachined Ultrasonic Transducer: CMUT) in which a vibrating part having the structure in which a cavity is sandwiched between upper and lower layer electrodes is formed on a silicon substrate has been currently developed.
Compared with the ultrasonic transducer using the piezoelectric body, the CMUT has advantages such as wide usable ultrasonic frequency range and high resolution. Moreover, since the CMUT is manufactured by using LSI (Large Scale Integration) processing techniques, microfabrication thereof is possible. Therefore, the CMUT is particularly suitable for the case where one ultrasonic element is arranged in an array and the row or the column thereof is controlled or the case where both of them are controlled. In addition, since the ultrasonic element is formed on a Si (Silicon) substrate like a normal LSI, the CMUT has another advantage that a signal processing circuit for transmitting/receiving ultrasonic waves can be mounted together on one semiconductor chip.
Techniques relating to the CMUT are disclosed in, for example, U.S. Pat. No. 6,271,620 B1 (Patent Document 1).
Moreover, Japanese Unexamined Patent Application Publication No. 2006-333952 (Patent Document 2) discloses a method in which, when a short-circuited CMUT cell is detected, only the upper electrode channel of a normal CMUT cell group is connected to signal input/output lines without connecting the upper electrode channel that includes the defective CMUT cell to the signal input/output lines.
Japanese Unexamined Patent Application Publication No. 2006-343315 (Patent Document 3) discloses a method in which an upper electrode part (spoke) connecting mutually-adjacent CMUT cells to each other serves as a fuse, the fuse is cut off by a large current that flows when the CMUT cell is short-circuited, and the electrical connection to the short-circuited CMUT cell is stopped, thereby removing only the short-circuited CMUT cell.